The present invention relates to a blade/vane cascade segment, a blade/vane cascade, a stage, and a blade/vane channel of a turbomachine, as well as a turbomachine.
Turbomachines (such as gas and steam turbines) generally have a flow channel for conducting a fluid. The flow channel, which is also called an “annular space”, is bounded radially inward by the shaft of a rotor and radially outward by a casing; the designations “radially” as well as “axially” and “peripheral direction”, and terms derived therefrom are to be understood with reference to an axis of rotation of the rotor in this document, as long as nothing is indicated to the contrary.
Blade/vane cascades (for which the term “blade/vane ring” is also common) are arranged in the annular space of a turbomachine. They each comprise guide vanes or rotating blades that lie one behind the other in the peripheral direction at substantially regular distances, as well as stages belonging thereto, which are also called “cover plates”, and that usually each have a stage edge on the inflow side and one on the outflow side. These stage edges bound the stage surface in the axial direction; by “stage surface” is meant in this document the surface of the stage facing the annular space.
In this document, the stage edge “on the inflow side” is designated as the stage edge where the leading (axial) principal flow first passes through the annular space of the turbomachine during operation; correspondingly, the stage edge “on the outflow side” is the opposite-lying edge. The indications “downstream” or “upstream”, respectively, refer correspondingly to the axial principal flow direction, and thus only to the axial position, regardless of a possible displacement in the peripheral or radial direction: In particular, in this document, a point is to be understood as lying “downstream of the inflow or leading edges” (or “downstream of another point”), if it is arranged displaced axially in/with the direction of principal flow (i.e., following it) relative to a direct connection line between the leading edges (with one another) at the stage surface (or relative to the other point); the same applies to the term “upstream” (with opposite direction).
The section of the stage surface that is bounded in the axial direction by the direct connections (i.e., running in the peripheral direction without axial deviations) of the leading edges or the trailing edges, respectively, of adjacent blade/vane elements at the stage surface and by the pressure side of the one blade/vane element and the suction side of the other one, is called in this document a “blade/vane intermediate strip”. The width of the blade/vane intermediate strip in the peripheral direction at the leading edges is called the “pitch distance” (of the blade/vane cascade or a blade/vane cascade segment or the blade/vane elements). It can be measured, in particular, as the distance between the leading edges of adjacent blades/vanes in the peripheral direction in the region of the stage surface. The distance between the leading edges of the blade/vane elements and the trailing edges thereof that is measured (solely) in the axial direction (the direction of the provided axial principal flow) is called (axial) “cascade span”.
The pressure side of a blade/vane element and the suction side of an adjacent blade/vane element each bound a so-called blade/vane channel in the peripheral direction. In the radial direction, this blade/vane channel is bounded by so-called side walls within the turbomachine. These side walls are each formed, on the one hand, by the stages, and, on the other hand, by sections lying radially opposite to these stages: In the case of rotating blades, such a side wall is here a radially outer-lying section (in particular, a section of the casing); in the case of guide vanes, it is a radially inner-lying section (in particular, of a rotor hub).
A fluid flow conveyed through a flow channel is periodically influenced by the surfaces of the side walls. Flow layers that run close to these surfaces are more strongly diverted here, due to their slower speed, than flow layers that are further away from the side walls. Thus, a secondary flow that is superimposed on an axial principal flow arises and, in particular, leads to vortexes and pressure losses.
In order to reduce secondary flows, contouring is frequently introduced in the side walls in the form of elevations and/or depressions.
Many of these types of so-called “side wall contouring” are known from the prior art. By way of example, the patents or patent applications of the Applicant will be named: EP 2 487 329 B1, EP 2 787 172 A2, and EP 2 696 029 B1. The last-named publication discloses therein a blade/vane cascade with a side wall contouring that has a pressure-side elevation and a suction-side depression, wherein a highest section of the elevation and a lowest section of the depression lie in a region from 30% to 60% of the extension of the blade/vane elements in the axial direction and differ from one another by a maximum 10% in the axial direction.
Document EP 2 136 033 A1 discloses a side wall contouring in which a depression is arranged between every two blade/vane elements, forming a gutter in the stage surface.
From EP 2 423 444 A2 there is known a side wall contouring in which an elevation is arranged on the pressure side of a first blade/vane element and a depression extends parallel to the suction side of an adjacent blade/vane element. The elevation and the depression form a curved channel in this case.
EP 3 064 706 A1 discloses a series of guide vanes with vane channels of different configuration.